1. Field of the Invention
The present invention relates to sports or athletic shoes, and in particular, to an athletic shoe constructed to minimize impact shock and to maximize lateral stability.
2. Prior Art
The modern shoe, particularly an athletic shoe, is a combination of many elements which have specific functions, all of which must work together for the support and protection of the foot. The design of an athletic shoe has become a highly refined science. Athletic shoes today are varied in both design and purpose. Tennis shoes, racquetball shoes, basketball shoes, running shoes, baseball shoes, football shoes, weightlifting shoes, walking shoes, wrestling shoes, etc., are all designed to be used in very specific, and very different, ways. They are also designed to provide a unique and specific combination of traction, support, and protection to enhance performance. Not only are shoes designed for specific sports, they are also designed to meet the specific characteristics of the user. For example, shoes are designed differently for heavier persons than for lighter persons; differently for wide feet than for narrow feet; differently for high arches than for low arches, etc. Some shoes are designed to correct physical problems, such as over-pronation, while others include devices, such as ankle supports, to prevent physical problems from developing. It is therefore important to be able to adjust the characteristics of the various functional components of the shoe to accommodate these factors.
Generally, a shoe is divided into two parts, an upper and a sole. The upper is designed to snugly and comfortably enclose the foot. The sole is designed to withstand many miles of running. It must have an extremely durable bottom surface for contact with the ground. However, since such contact may be made with considerable force, protection of the foot and leg demands that the sole also perform a shock-absorbing function. It therefore typically includes a resilient, energy-absorbent material as a midsole in addition to the durable lower surface. This is particularly true for training or jogging shoes designed to be used over long distances and over a long period of time.
Extensive clinical evaluation of foot and knee injuries sustained by, for example, runners and joggers, suggests that the most important factors associated with such injuries are shock absorption on impact and lateral foot stability. Based on injury data, these two factors appear to be of about equal importance. Therefore, both factors should be carefully considered in any improvements in athletic shoes.
For most runners, initial foot impact occurs in the heel region. Therefore, the heel strike cushioning material, which is contained principally in the midsole of a running shoe must have a firmness which provides for proper impact cushioning for a person of about average weight. When the runner is heavy, the heel cushioning material may "bottom out" before heel impact is completely absorbed, and shock-related injuries can result. On the other hand, if the cushioning material is too soft, poor lateral foot stability may result in injuries. As a general rule, athletic shoes, for example running shoes, which have a relatively firm midsole, particular in the heel region, provide the best lateral stability.
Most sports include some running, though many sports place additional demands upon the shoe which are performance and/or injury related. Jump-land activities such as basketball, volleyball and aerobics typically produce forefoot impact forces due to initial forefoot contact followed shortly thereafter by greater rearfoot impact forces. These forces, either singularly, but more often cumulatively, can result in various lower extremity injuries. These activities also often incorporate mild to excessive side-to-side motions that require a stable foot platform, i.e., a stable shoe, for successful and injury free performance. These requirements are somewhat functionally similar to those of running but produce greater demands upon both the shoe and the lower extremities.
Shock to the foot, ankle, and leg maybe considered herein to be substantially vertically directed, and is directly proportional to the rate of vertical deceleration which the foot experiences during a footfall as well as a function the knee angle/action of the knee. In running, sequential impacting of first the lateral heel region in a foot, and thereafter the forefoot region, results in what might be thought of as a dual-peak shock-transmission situation. In other words, vertical foot deceleration tends to maximize in concurrence with these two events. Accordingly, shock absorption and reduction is directly attainable by minimizing the peaks of such peak deceleration by the use of a combination of heel strike, medial motion control, and forefoot cushioning elements. In landing from a jump the sequence occurs in reverse order.
There are many limiting factors in the design of a cushioned midsole for protection against foot and knee injuries, among them being the range of suitable cushioning materials. Current commercial cushioned midsoles comprise elastomeric foam, such as ethylene vinyl acetate (EVA) foam, within a narrow mid-range of hardness, or an elastomeric foam within which a gas-filled membrane is encapsulated. The use of elastomeric foam material by itself is limited to foams of relatively higher density and hardness, because low density and hardness foams are too soft and bottom out too quickly, i.e., collapse to a point where they no longer functions as a shock absorber under relatively low force, and also because low hardness foams provide very little lateral stability. Hence, prior art commercial midsoles have generally been limited to higher density, relatively hard foams, a compromise between cushioning and stability. The use of a softer foam provides additional cushioning at a sacrifice to lateral stability. Conversely, the use of a harder foam enhances lateral stability at a sacrifice to cushioning.
The use of a cushioning system comprised of a membrane partitioned into a plurality of chambers which are filled with a gas, which in turn are incorporated into a foam midsole, improves the cushioning capability of the midsole over that of conventional EVA-foam because it does not bottom out as rapidly; however, problems exist with respect to such cushioning systems, e.g. leakage, etc.
Additionally, gel filled cushioning elements are wellknown in the art. For example, U.S. Pat. No. 4,768,295, to Ito, describes gel cushioning members having a plurality of chambers mounted in the recesses of sole plates. When the cushioning member is put in the recess formed in the sole plate, air chambers are formed between the filled chambers and the bottom of the recess. The air in the air chambers is compressed as the sole plate and the cushioning members are deformed by shock upon landing. The compressed air functions as a repulsion force when kicking. See also U.S. Pat. Nos. Des. 300,084 and Des. 300,085 to Ito et al. and 297,381 to Sugiyama. Shoes containing such gel packs are sold by ASICS Tiger Corporation, Fountain Valley, Calif.
Additional prior art references relevant to this invention are:
U.S. Pat. No. Des. 297,980, to Sugiyama, describes a cushioning for a shoe midsole comprised essentially of one cell having partition walls therein.
U.S. Pat. No. 3,765,422, to Smith, relates to a fluid cushion podiatric insole in the form of a flat envelope in the outline of the wearer's foot and containing a semi-liquid/solid particulate material as a flowing cushioning medium. The insole is provided with transverse dividers (ribs) which divide the insole into front and rear chambers, and longitudinal dividers which serve as flow directing wall formations.
U.S. Pat. No. 4,309,832, to Hunt, describes hinge joints in the sole of a shoe.
U.S. Pat. Nos. 4,342,157 and 4,472,890, to Gilbert, describe the use of liquid-filled shock absorbing cushions in the heel portion and forefoot portion of a shoe. Typical liquids include water, glycerine, and mineral oil.
U.S. Pat. No. 4,506,461; 4,523,393; and 4,322,892, to Inohara, describes a sports shoe sole wherein an interlayer body is provided at the heel portion with an air inclusion means such as grooves and apertures that open at least to one side of the interlayer body. The air inclusion portions open externally at each of the sides of the shoe.
U.S. Pat. No. 4,535,553, to Derderian et al., discloses a shock-absorbing sole member comprised of an insert member and elastomeric foam encasing the insert member. The insert member is formed of resilient plastic material and includes a plurality of transversely and longitudinally spaced discreet shock-absorbing projections.
U.S. Pat. No. 4,567,677, to Zona, relates to a water and air filled shoe insole having flow restrictions so as to restrict the flow of water and air from the metatarsal area and heel area and vice versa. The flow restrictions are said to provide a massaging action for the foot of the user.
U.S. Pat. No. 4,610,099, to Signori, describes a shock-absorbing shoe sole which provides adjustably inflated pneumatic support at the rear half of the sole by an inflatable bladder therein. A removable in-sole panel provides access for repair and/or replacement of the bladder. The bladder may have the upper and lower panel locally bonded or tufted at longitudinally and laterally spaced points to avoid the tendency to balloon when pressurized.
U.S. Pat. No. 4,763,426, to Polus et al., describes a sports shoe with a sole which has air chambers which accept air at positive pressure and a foot operated pneumatic inflating device connected thereto.
U.S. Pat. No. 4,815,221, to Diaz, describes a shoe having an energy control system for shock absorption and for propulsion of the wearer. The energy control system includes a spring system and an overlying energy absorbing member located in a cavity in the midsole.
U.S. Pat. No. 4,817,304, to Parker et al., describes a sole member which includes a sealed inner member of a flexible material which is inflated with a gaseous medium to form a compliant and resilient insert. An elastomeric yieldable outer member encapsulates the insert about preselected portions of the insert. On the sides is a gap, i.e., opening, which permits the insert to expand into the gap during foot impact. The shoe may be designed such that the sides of the insert are at least flush with and preferably extend beyond the sides of the shoe (see FIG. 4). Additional gaps may be provided in the forefoot area.
U.S. Pat. No. 4,833,795, to Diaz, describes a shoe having a pivot surface located in the ball portion of the forefoot region to facilitate pivoting as the foot contacts the ground. The pivot surface defines a cushioning air pocket between the outsole and the midsole.
U.S. Pat. No. 4,856,208, to Zaccaro, describes a shoe sole which includes two inflatable tubes that extend along the sides of the body portion of the shoe or a single inflatable tube that extends around the periphery of the body portion so as to define an elongated recess that exposes the bottom surface of the body portion, the fluid in the inflatable tubes moving therewithin when more load is applied on one side of the shoe defining use than the other.
U.S. Pat. No. 4,887,367, to Mackness et al., describes the use of resilient spherical bodies within recesses in the front portion and/or the heel portion of the sole of a shoe. The hardness of the resilient bodies can be adjusted to enhance the elasticity of the soles of the shoe by virtue of the fact that the spherical bodies can be inflated and deflated or can be replaced.
European Patent Application, Publication No. 0 298 449 to Litchfield, describes the midsole of a shoe having an elastomeric material which has a number of spaced apart horizontal tubes extending the width of the midsole which are encapsulated in the elastomeric material. The tubes are hollow and lay side-by-side in a direction either perpendicular to the longitudinal axis of the shoe, parallel to the axis, or in any other direction functional for foot and shoe mechanics. The tubes are preferably encapsulated by the polyurethane material including encapsulation of the end of the tubes to prevent easy collapse thereof.
Patents which illustrate visible cushion means include, for example, Yung-Mao (U.S. Pat. Nos. 4,843,741 and 4,974,345 and Swartz et al. (U.S. Pat. No. 4,972,611).